The present invention relates to micromirrors for micro-electro-mechanical systems (MEMSs). More particularly, the present invention relates to micromirrors using doped aluminum layer and methods of fabricating the same.
New advancements in projection systems utilize an optical semiconductor known as a digital micromirror device. A digital micromirror device chip is one of the most sophisticated light switches in the field. It contains an array of 750,000 to 1.3 million pivotally-mounted microscopic mirrors. Each mirror may measure less than ⅕ of the width of a human hair and corresponds to one pixel in a projected image. The digital micromirror device chip can be combined with a digital video or graphic signal, a light source and projector lens so that the micromirrors reflect an all-digital image onto a screen or other surface.
US patent publication No. 2004/0223240 discloses micromirror arrays having a reflective layer comprising gold, silver, titanium, or aluminum. The micromirror optimizes the contrast ratio of the micromirror array so that when the micromirrors are in their ‘off’ state they send minimal light to the spatial region where light is directed when micromirrors are in their ‘on’ state.
U.S. Pat. No. 6,778,315 discloses a Micro mirror structure with flat reflective coating. Each mirror includes a substrate, a diffusion barrier layer located above the substrate, and a reflective layer located above the diffusion barrier layer. The reflective layer comprises gold, silver or aluminum.
U.S. Pat. No. 6,800,210 discloses a method for making a micromechanical device by removing a sacrificial layer with multiple sequential etchants. The micromechanical device uses metal such as gold, silver or aluminum as reflective layer.
Conventional micromirrors often include hillocks (raised feature or bumps) or voids in the reflective layer. The hillocks or voids may however cause artifacts or distortions in the projected image. Conventional micromirrors also tend to have unstable light-reflecting characteristics, possibly resulting from large surface roughness of the reflective layer.